1. Field of the Invention
The present invention relates generally to an evaporative type cooling system for an internal combustion engine wherein liquid coolant is permitted to boil and the vapor used as a vehicle for removing heat therefrom, and more specifically to such a system which minimizes the total amount of liquid coolant which is required for all modes of operation (including non-use) and which simultaneously obviates rusting of essentially all of the components of the system prone to oxidation by atmospheric oxygen.
2. Description of the Prior Art
In currently used "water cooled" internal combustion engines liquid is forcefully circulated by a water pump, through a cooling circuit including the engine coolant jacket and an air cooled radiator. This type of system encounters the drawback that a large volume of water is required to be circulated between the radiator and the coolant jacket in order to remove the required amount of heat.
Due to the large mass of water inherently required, the warm-up characteristics of the engine are undesirably sluggish. For example, if the temperature difference between the inlet and discharge ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of water may effectively remove from the engine under such conditions is 4 Kcal. Accordingly, in the case of an engine having an 1800 cc displacement (by way of example) operated full throttle, the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this, a flow rate of approximately 167 liter/min must be produced by the water pump. This of course undesirably consumes several horsepower produced by the engine. Further, the weight of the large amount of coolant adds undesirably to the overall weight of the vehicle.
Japanese Patent Application Second Provisional Publication No. Sho. 57-57608 discloses an arrangement which has attempted to vaporize a liquid coolant and use the gaseous form thereof as a vehicle for removing heat from the engine. In this system the radiator and the coolant jacket are in constant and free communication via conduits whereby the coolant which condenses in the radiator is returned to the coolant jacket little by little under the influence of gravity.
This arrangement, while eliminating the power consuming coolant circulation pump which plagues the above mentioned arrangement, has suffered from the drawbacks that the radiator, depending on its position with respect to the engine proper, tends to be at least partially filled with liquid coolant. This greatly reduces the surface area via which the gaseous coolant (for example steam) can effectively release its latent heat of vaporization and accordingly condense, and thus has lacked any notable improvement in cooling efficiency. Further, with this system, in order to maintain the pressure within the coolant jacket and radiator at atmospheric level, a gas permeable water shedding filter is arranged to permit the entry of air into and out of the system.
However, this filter permits gaseous coolant to readily escape from the system, inducing the need for frequent topping up of the coolant level. A further problem with this arrangement is that some of the air, which is sucked into the cooling system as the engine cools, tends to dissolve in the water, whereby upon start up of the engine, the dissolved air tends to come out of solution and forms small bubbles in the radiator which adhere to the walls thereof and form an insulating layer. The undissolved air also tends to collect in the upper section of the radiator and inhibit the convection-like circulation of the vapor from the cylinder block to the radiator. This of course further deteriorates the performance of the device.
When the engine is not in use, the air which is permitted into the system via the air-permeable filter tends to induce rapid corrosion of particularly the upper sections of the radiator which are not immersed in liquid coolant due to exposure to atmospheric oxygen. Thus, because the system is not completely filled with coolant, as in the case of the circulation type systems, the addition of anti-corrosive agents to the coolant cannot prevent rapid deterioration of the exposed sections of the radiator and the like.
European Patent Application Provisional Publication No. 0 059 423 published on Sept. 8, 1982 discloses another arrangement wherein liquid coolant in the coolant jacket of the engine is not forcefully circulated therein and permitted to absorb heat to the point of boiling. The gaseous coolant thus generated is adiabatically compressed in a compressor so as to raise the temperature and pressure thereof and thereafter introduced into a heat exchanger (radiator). After condensing, the coolant is temporarily stored in a reservoir and recycled back into the coolant jacket via a flow control valve.
This arrangement has suffered from the drawback that when the engine is stopped and cools down the coolant vapor condenses and induces sub-atmospheric conditions which tend to induce air to leak into the system. This air tends to be forced by the compressor along with the gaseous coolant into the radiator.
Due to the difference in specific gravity, the above mentioned air tends to rise in the hot environment while the coolant which has condensed moves downwardly. The air, due to this inherent tendency to rise, tends to form pockets of air which cause a kind of "embolism" in the radiator and badly impair the heat exchange ability thereof.
FIG. 1 shows an evaporative type cooling system described in U.S. Pat. No. 4,367,699 issued on Jan. 11, 1983 in the name of Evans. This arrangement features a separation tank 6 wherein gaseous and liquid coolant are initially separated. The liquid coolant is fed back to the cylinder block 7 under the influence of gravity while the relatively dry gaseous coolant (steam for example) is condensed in a fan cooled radiator 8.
The temperature in the radiator is controlled to a predetermined constant level by selective energizations of the fan 9 which maintains a rate of condensation therein sufficient to provide a liquid seal at the bottom of the device. Condensate discharged from the radiator via the above mentioned liquid seal is collected in a small reservoir-like arrangement 10 and pumped back up to the separation tank via a small constantly energized pump 11.
This arrangement, while providing an arrangement via which air can be initially purged to some degree from the system, tends to suffer from rapid loss of coolant when operated at relatively high altitudes, due to the nature of the arrangement which permits said initial non-condensible matter to be forced out of the system. Once the engine cools, air is relatively freely admitted back into the system. The provision of the bulky separation tank 6 also renders engine layout difficult, increases the weight of the system and induces the additional problem that the level of coolant in the coolant jacket cannot be assuredly maintained under all modes of engine operation.
When the engine is stopped or "shut-down", as the condensor is completely drained of coolant and filled with atmospheric air and the level of coolant in the separation tank lowered, the interior of the condensor, separation tank and conduiting etc., are subject to rapid corrosion due to exposure to the oxygen in the air. This corrosion tends to rapidly reduce the usable life of the system and requires troublesome and expensive parts replacement from time to time. The addition of anti-corrosive agents to the coolant does not alleviate the problem.
Japanese Patent Application First Provisional Publication No. 56-32026 discloses an arrangement wherein the structure defining the cylinder head and cylinder liners is covered with a porous layer of ceramic material and wherein coolant is sprayed into the cylinder block from shower-like arrangements located above the cylinder heads. The interior of the coolant jacket defined within the engine proper is essentially filled with gaseous coolant during engine operation at which time liquid coolant is sprayed onto the ceramic layers.
This arrangement, while requiring very little liquid coolant, has proven totally unsatisfactory in that, upon boiling of the liquid coolant absorbed into the ceramic layers, the vapor thus produced and which escapes toward and into the coolant jacket, inhibits the penetration of fresh liquid coolant into the layers and induces the situation wherein rapid overheat and thermal damage of the ceramic layers and/or engine soon results. Further, this arrangement is of the closed circuit type and is plagued with air contamination and blockages in the radiator similar to the compressor-equipped arrangement discussed above.
FIG. 2 shows a system disclosed in U.S. Pat. No. 1,787,562 published on Jan. 6, 1931 in the name of L. P. Barlow. In this arrangement the coolant vapor which is condensed in the radiator 16 is first collected in the lower tank 17 of the radiator 16 and then transferred to a larger reservoir 18. The collected coolant is returned to the coolant jacket 20 via a pump 22 which is controlled by a float type level sensor arrangement disposed in the upper section thereof.
The pump 22 communicates with the coolant jacket 20 via a conduit 24 which is formed with a U-bend 25. This bend limits the amount of coolant which can drain back through the conduit 24 toward the reservoir 18. The interior of the radiator 16 and the reservoir 18 are both vented to the atmosphere via a conduit 26 and vent port 27 arrangement which fluidly interconnects the top of the reservoir 18 with lower tank 17 of the radiator.
Accordingly, this arrangement also suffers from the problem that during non-use the interior of the radiator 16 and the upper section of the engine coolant jacket 20 are constantly exposed to atmospheric oxygen and accordingly prone to undergo rusting and the like deterioration. A further drawback encountered with this device is that the cooling fan 28 is constantly driven by the engine and not controlled in response to the amount of heat actually produced by the engine and thus is apt to consume unecessary energy.
FIG. 3 shows an arrangement which is disclosed in U.S. Pat. No. 4,549,505 issued on Oct. 29, 1985 in the name of Hirano. The disclosure of this application is hereby incorporated by reference. For convenience the same numerals as used in the above mentioned patent are also used in FIG. 3.
While solving many of the drawbacks encountered with the previously disclosed prior art by completely filling the interior of the coolant jacket, radiator and associated conduiting which define the closed loop cooling circuit, with liquid coolant when the engine is not in use and effecting steps which purge any air which may leak in with the passing of time or during modes of operation when the pressure in the cooling circuit is rendered subatmospheric, this arrangement has itself suffered from the drawbacks that it requires a relatively large amount of liquid coolant and a correspondingly large reservoir. This increases the weight of the system undesirably. The system also employs no less than four electromagnetic valves to enable the required coolant management to be effected. This, while permitting the variation of the temperature at which the coolant boils with respect to the instant engine speed and load, notably increases the complexity and cost of the system.
Further, in the event that one of the valves malfunctions, the operability of the whole system is apt to be placed in jeopardy and likely to result in engine damage or temporary inoperability.